Automotive-type alternators typically are three-phase alternators which, to provide d-c power to a battery, are usually associated with rectifier structures to provide the required d-c output. For ease of assembly and maintenance, and to provide a direct d-c output at the housing of the alternator itself, the rectifier structures are usually positioned within the alternator housing. They are cooled by the cooling air drawn through the alternator by a fan assembly, customarily rotating with the alternator shaft. Basically, the three-phase alternator usually has fixed armature windings and a rotating field. In the customarily used alternator, the field is externally excited and receives its current through a pair of slip rings. The current supply to the slip rings is controlled by a voltage regulator. Ordinarily, six power rectifier diodes are used, connected in a rectifying bridge circuit to the output terminals of the alternator phase windings which, usually, are star-connected, although the connection may also be of the delta-type. Three additional rectifier diodes may be provided to supply rectified d-c to the exciter field of the alternator. If the alternator is designed for extremely high power supply, the rectifier diodes may, themselves, consist of parallel connected diode elements. The six power diodes are subdivided into three negative diodes and three positive diodes which, respectively, with their cathodes and anodes are connected to an associated bus, so that the outputs from the diodes can be directly connected to the positive terminal and to the negative terminal--typically ground or chassis--of the generator. The free terminals of respective negative and positive diodes are then connected to a phase terminal of the armature winding, so that the power diodes are connected in a full-wave rectifying bridge circuit.
The rectifier diodes customarily used are semiconductor elements which have a limited operating temperature range. In operation, they generate heat which must be reliably dissipated to prevent heating of the diodes above a predetermined temperature. Usually, the diodes are associated with heat sinks which often are shaped as two or three separate sheet metal heat dissipated elements. Larger size three-phase alternators may have rectifier systems with three separate heat sinks or heat dissipating plates. The electrical connection with the armature windings is then effected by a wire bridge or over a heat dissipating sheet metal element itself. Usually, the sheet metal elements are so located that their major plane is transverse to the direction of cooling airflow. This is undesirable from the point of view of airflow and also is relatively inefficient with respect to heat dissipation or cooling of the heat dissipating element as such. If massive metal heat sinks are used, particularly if additionally furnished with fins, cooling is enhanced but the starting materials, as well as manufacture, is expensive. Additionally, assembly is labor-intensive and thus likewise costly.